CNAV-2电文软判决译码实现与性能分析

Implementation and performance analysis of soft-decision decoding of CNAV-2 message

第3代GPS民用信号L1C的CNAV-2电文采用了LDPC编码以提高电文解调性能。由于传统接收机常用的硬判决译码不能充分利用信道信息,探讨了译码性能更优的软判决译码方法。首先仿真分析了适合L1C接收机的软判决译码算法及其性能和复杂度,表明软判决译码能够提供比硬判决高2~3 d B的编码增益。然后设计了完整的CNAV-2电文译码方案,包括帧同步、LDPC和BCH译码、解交织、CRC校验和相干合并策略及流程,并在软件接收机上得以实现。最后通过实际QZSS卫星信号和商用射频GNSS模拟器信号验证了设计的正确性。

The CNAV-2 navigation message of the 3rd generation GPS civilian signal L1 C adopts LDPC coding to improve demodulation performance. Since the hard-decision decoder traditionally employed in receivers can not fully use the channel information, several soft-decision-based decoding methods are explored to achieve better performance in this paper. The paper first analyzes the soft-decision LDPC decoding algorithms applicable to L1 C receivers, calculates their complexity, and simulates their performance. The results show a 2~3 d B gain of the soft-decision decoding relative to the hard-decision. Then the whole scheme of CNAV-2 message decoding is designed and implemented in our software receiver, including frame synchronization, symbol de-interleaving, BCH and LDPC decoding, CRC checking, and coherent combination. Finally, the correctness of the design is validated by using the signals from the true QZSS satellite as well as a commercial RF GNSS signal simulator.